Contact Image Sensor (CIS) Technology
CIS Technology Overview
When using conventional CCD linear image sensors for document scanning, a lens is required, which can potentially lead to image distortions like pin cushion distortion, especially when dealing with larger documents. In contrast, scanning with Contact Image Sensor (CIS) technology produces distortion-free images at a 1:1 ratio. The contact image sensor advantages of greater clarity, greater affordability over the years, and lower power consumption make the CIS scanner the preferred technology of choice.
Scanning Methods for Contact Image Sensors
There are two types of scanning methods:
1) Sheetfed type:
The document sheet is fed though the module by a roller.
2) Flatbed type:
The document stays flat on a glass bed while the module moves across the whole sheet.
CIS Structure and Components
Contact image sensors are composed of the following components:
1) Sensor Array and Printed Circuit Board (PCB)
The sensors are aligned and mounted on a PCB with other passive components. Sensors’ characteristics define the key features of the CIS, such as resolution, scanning speed, sensitivity, MTF, etc.
2) Light Source – Provides illumination for image scanning
There are two types of illumination:
Light Bar is for high-speed contact image sensors, it consists of array of LEDs evenly on a PCB.
Light Guide is for low-speed contact image sensors, it has acrylic rod to convey uniform illumination from LED(s).
Number of light sources may differ depending on the application:
Single-light is suitable for low speed and low cost.
Dual-light is good for high speed and scanning wrinkled objects.
LED wavelengths/colors supported for light source: UV, R, G, B, NIR, and White
- UV (Ultra-Violet): 365 nm & 390 nm
- Visible: Red, Green, Blue
- NIR (Near-Infrared): 880 nm & 940 nm
3) Lens Array – To focus the image for scanning
This is sometimes called Rod Lens or SLA (SELFOC Lens Array). There are single-row or dual-row types available, dual-row is for better collimation. In addition to being constructed with glass material for better quality, the Rod lens can be made of plastic material as well.
4) Cover Glass – The focus point of the CIS is on the surface of the glass, which also serves as a protection.
5) Connector – The inputs/outputs of the CIS. A camera link cable is required to connect the CIS to a system to
receive the scanned image.
6) Housing – To house everything together, normally it is made of plastics, however, aluminum housing is also available for harsh environments.
* CMOS Sensor Inc supports custom CIS modules according to your project's requirements, in addition to the standard product lineup.
CMOS Sensor Inc. is a trusted designer and manufacturer of contact image sensors (CIS) and CIS modules with over 25 years of engineering excellence.